Abstract: β–O–4 is the most abundant linkage in the lignin structure. It is of great significance to convert lignin into monophenols by breaking the β−O−4 linkage. Therefore, β−O−4 dimer model compound was used as raw materials in this paper. The effects of metal catalysts, temperature, time and hydrogen pressure on the conversion of dimer and yield of monophenols were investigated by GC-MS, GC-FID, HSQC NMR characterization methods. The results show that NaOH and carbon-supported metal catalysts have a synergistic effect which can enhance the breakage of β−O−4 linkage, and the best promotion effect is obtained over Pd/C and NaOH with the monomer yield increases from 44.1% to 83.4%. NaOH and Pd/C can inhibit the removal of C_α−OH of the dimer and enhance the breakage of β−O−4 linkage effectively, leading to the increment in monomers. The NaOH and Pd/C catalytic system also shows excellent performance to the breakage of α−O−4. Under the best conditions, alkali lignin is converted into monophenols over NaOH and Pd/C with the yield of 37.5%, and the selectivity of benzyl alcohol is as high as 48%.